Morphological differences in Northwest Atlantic redfishes (Sebastes) are recognized but their biology is relatively unknown, due to the confusion associated with redfish systematics in past decades. For a redfish reproductive biology study we utilized historical sex and maturity data collected between 1957 and 1969. We applied the logistic model to estimate the size at maturity from 4501 S. marinus and 43 988 beaked redfishes (S. mentella and S. fasciatus combined) covering the whole Northwest Atlantic. The sizes at maturity for female redfishes were significantly larger than that of males for both S. marinus and beaked redfishes. The size at maturity in female S. marinus was significantly larger than that of beaked redfishes whereas in males there was no significant difference between groups. A geographic cline in size at maturity was noted in beaked redfishes, with a decreasing trend for S. mentella from Baffin Bay southward to the Gulf of St. Lawrence, and for S. fasciatus from the Grand Bank to the Nova Scotian Shelf.
Cutlassfishes, Trichiurus Linnaeus, 1758, are the most important commercial marine fish species of China in terms of weight and they are found in all Chinese waters. However, no study has been conducted on the populations of Trichiurus in the South China Sea. The aim of this study was to investigate the reproduction of the populations of Trichiurus spp. in the South China Sea. In a 12 mo sampling period between December 1996 and November 1997, 1495 specimens of T. lepturus and I.nanhaiensis were collected from Hong Kong coastal waters. Spawning period and reproductive cycle were studied by checking the temporal profile of the Relative Gonadal Index/Gonosomatic Index, and by examining ovaries macroscopically and whole oocytes microscopically. All 3 methods provided sim~lar results: the spawning periods of T, lepturus and T. nanha~ensis were March to June and April to August, respectively. Both species were found to practice group-synchronous spawning and mature females are capable of spawning more than once each spawning season. The mean preanal lengths at sexual maturity of T. lepturus and T. nanhaiensis females were 255 and 282 mm respectively. The sex ratios of both species were significantly different from 1:l among different sampling months, and different age and size ranges.
Separation by species of 199 sharp-beaked redfish, collected from northeastern Grand Bank and preliminarily assigned to Sebastes fasciatus or S. mentella on the basis of some subjective exterior characteristics, was confirmed by differences in the passage of the extrinsic gasbladder muscle between the ventral ribs and in its attachment to the vertebrae posteriorly. In S. fasciatus the gasbladder muscle passed between ventral ribs 3-4 in 94% of the specimens and between ribs 4-5 in 5%, whereas in all S. mentella the muscle passed between ventral ribs 2-3. Also, the posterior tendon of the gasbladder muscle in S. fasciatus commonly had three branches attached primarily to vertebrae 8, 9 and 10, whereas in S. mentella the tendons, usually not branched, was attached to vertebra 7.
Analysis of morphometric data for differentiating fish species and stocks has frequently been unsatisfactory as a result of sampling bias associated with the varying size of specimens and the large overlapping of characters. These difficulties may be overcome by using a discriminant function with covariance and multivariate analysis of covariance. In a classification study of beaked redfishes, in which the specimens of Labrador redfish (Sebastes fasciatus) are relatively smaller than those of deepwater redfish (S. mentella), a single character would not separate species, but a compound criterion (discriminant function) of several characters separated the species effectively. A discriminant function with covariance separated species/populations remarkably well and better than one without covariance. Seven morphometric characters were identified as pertinent discriminators between S. fasciatus and S. mentella. As much as 89% of the total variation in the sample was accounted for by the discriminant function and only 8 out of 198 individuals (4%) were in the zone of uncertainty. It is explained why using a large number of characters in discriminant analysis may not be appropriate for samples of limited sizes. Also, expressing morphometric measurements as ratios, proportions, or percentages of body length may not be an appropriate way of reducing variation owing to size differences.
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